Crude oil extracted from reservoir rock contain a number of undesired compounds, or contaminants. Reduction in the amount of sulfur compounds in automotive fuels and other refined hydrocarbons are required in order to meet environment concerns and regulations. These contaminants also adversely impact refinery operations, e.g., by poisoning catalysts.
Crude oils contain heteroatoms such as sulfur, nitrogen, nickel, vanadium and others in quantities that impact the refinery processing of the crude oils fractions. Light crude oils or codensates contain in concentrations as low as 0.01 W %. In contrast, heavy crude oils contain as much as 5-6 W %. The nitrogen content of crude oils can range from 0.001-1.0 W %. The heteroatom contents of typical Arabian crude oils are listed in Table 1 from which it can be seen that the heteroatom content of the crude oils within the same family increases with decreasing API gravity, or increasing heaviness.
TABLE 1PropertyASLAELALAMAHGravity, °51.439.533.031.127.6Sulfur, W %0.051.071.832.422.94Nitrogen, ppmw70446106414171651RCR, W %0.511.723.875.277.62Ni + V, ppmw<0.12.92134.067The following abbreviations are used in Table 1:ASL - Arab Super Light;AEL - Arab Extra Light:AL - Arab Light;AM - Arab Medium andAH - Arab Heavy;W % is percent by weight;ppmw is parts per million by weight.
The heteroatom content of the crude oil fractions also increases with increasing boiling point and representative data is provided in Table 2.
TABLE 2Fractions, ° C.Sulfur WT %Nitrogen ppmwC5-900.01 93-1600.03160-2040.06204-2600.34260-3151.11315-3702.00253370-4302.06412430-4822.65848482-5703.091337
These impurities must be removed during the refining operations to meet the environmental regulations for the final products (e.g., gasoline, diesel, fuel oil) or for the intermediate refining streams that need to be processed for further upgrading, such as reforming isomerization.
In a typical petroleum refinery, crude oil is first fractionated in an atmospheric distillation column to separate and recover sour gas and light hydrocarbons, including methane, ethane, propane, butanes and hydrogen sulfide, naphtha (36-180° C.), kerosene (180-240° C.), gas oil (240-370° C.), and atmospheric residue, which is the remaining hydrocarbon fraction boiling above 370° C. The atmospheric residue from the atmospheric distillation column is typically used either as fuel oil or sent to a vacuum distillation unit, depending on the configuration of the refinery. The principal products of vacuum distillation are vacuum gas oil, being hydrocarbons boiling in the range 370-520° C., and vacuum residue consisting of hydrocarbons boiling above 520° C.
Contaminants such as sulfur, nitrogen and polynuclear aromatics in the crude oil fractions impact these downstream processes, and others, including hydrotreating, hydrocracking and FCC. These contaminants are present in the crude oil fractions in varying structures and concentrations.
Naphtha, kerosene and gas oil streams derived from crude oils or from other natural sources such as shale oils, bitumens and tar sands, are treated to remove the contaminants, e.g., mainly sulfur, whose quantity exceeds the specifications. Hydrotreating is the most common refining process technology employed to remove the contaminants. Vacuum gas oil is typically processed in a hydrocracking unit to produce gasoline and diesel or in a fluid catalytic cracking unit to produce gasoline, with LCO and HCO as by-products. The LCO is typically used either as a blending component in a diesel pool or as fuel oil, while the HCO is typically sent directly to the fuel oil pool. There are several processing options for the vacuum residue fraction, including hydroprocessing, coking, visbreaking, gasification and solvent deasphalting.
Processes have been disclosed employing solid adsorbent materials for use in treating hydrocarbon feedstreams to remove undesired compounds, including nitrogen and sulfur-containing compounds. For example, U.S. Pat. No. 4,846,962 discloses a process for selectively removing basic nitrogen compounds from solvent extracted oils by their absorption on a solid acidic polar-adsorbent material. Following the solvent extraction process, the basic nitrogen compounds present with the desired oil fraction are contacted with adsorbents of the silica-alumina type, Ketjen high-alumina base (amorphous) and H—Y zeolite (crystalline) identified as being preferred. In addition, various treatments were applied to the adsorbents to improve their effectiveness. It was also disclosed that the adsorbents could be regenerated, e.g., by purging with a hot hydrogen gas stream.
In the process described in U.S. Pat. No. 5,843,300, organic sulfur compounds, especially aromatic sulfur compounds, are removed from an FCC feedstream with minimal adsorption of aromatic hydrocarbons using a zeolite X exchanged with alkali or alkaline earth cations, with KX being an especially effective adsorbent. It was also indicated that the adsorbent could be regenerated by contact with a heated stream of hydrogen. The use of the process in treating FCC feedstocks having particular classes of sulfur-containing materials was disclosed as particularly effective.
A process is disclosed in U.S. Pat. No. 6,248,230 for improving the efficiency of hydrodesulfurization processes by first extracting natural polar compounds from a distillate feedstream. The improvement was based upon the stated finding that even small quantities of natural polar compounds have a significant negative effect upon the hydrodesulfurization process in the deep desulfurization zone. The natural polar compounds includes nitrogen and sulfur-containing compounds having a relatively higher polarity than that of dibenzothiophene. Adsorbents include activated alumina, acid white clay, Fuller's earth, activated carbon, zeolite, hydrated alumina, silica gel, ion exchange resin, and their combinations. In the process disclosed, the treated feedstream is catalytically hydroprocessed to produce a hydrocarbon fuel.
Removal of contaminants depends on their molecular characteristics; therefore, detailed knowledge of the sulfur species in the feedstock and products is important for the optimization of any desulfurization process. Numerous analytical tools have been employed for sulfur compounds speciation. Gas chromatography (GC) with sulfur-specific detectors is routinely applied for crude oil fractions boiling up to 370° C. The use of ultra-high resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry has recently been advanced as a powerful technique for the analysis of heavy petroleum fractions and whole crude oils. Use of this methodology is described in (1) Choudhary, T. V. Malandra, J., Green J., Parrott, S., Johnson, B., Angew. Chem., Int. Ed. 2006, 45, 3299-3303; (2) Hughey, C. A., Rodgers, R. P., Marshall, A. G., Anal. Chem. 2002, 74, 4145-4149; and (3) Müller, H., Schrader, W., Andersson, J. T., Anal. Chem., 2005; 77, 2536-2543.
Two ionization analytical methods that have been successfully employed in the analysis for aromatic sulfur and polar nitrogen petroleum components are electrospray ionization (EST) and atmospheric pressure photo ionization (APPI). Both are well known analytical methods and the apparatus for their practice are commercially available.
From the above discussion, it is apparent that it would be desirable to upgrade crude oil by removing specific undesirable compounds at an early stage of processing so that the fractions subsequently recovered are free of these compounds.
It is therefore a principal object of the present invention to provide a novel method of treating crude oil to substantially reduce the content of undesired sulfur and nitrogen compounds.
Another object of the invention is to provide a method of removing undesired sulfur and nitrogen compounds from crude oil that requires a relatively low capital investment for equipment and that is economical to operate.